Shutting down GC at end of day

[GC_User]

Hey all.

I run a 6890 GC with H2 carrier gas and an FID hooked up to only cylinders. In order to conserve the air we use for the detector I am considering having the GC automatically shut down after completing the sample queue. Are there any hazards in this? The oven will cool down to ambient temp, the carrier gas will not flow through the column and the detector will turn off. Am I missing anything?

[AICMM]

GC_user,

I would never turn off the carrier to a GC that is turned on. Not worth it. If you turn off the detector, you then have a controlled hydrogen leak. If that is okay, then turning off the fuel air is an option. Is cylinder air really that expensive?

Best regards.

[DR]

^ I agree. I know zero grade air isn't cheap.

Even over weekends, I'd tend to leave at least a modest flow of carrier gas running if you're using capillary columns. If you're planning to run samples on a daily basis during the week, I'd probably leave the detector on over night as well.

[Consumer Products Guy]

Us:
We have air purifier for the GC FIDs. We have hydrogen generator for the FIDs, have not yet used that for carrier. We turn those off when not in use. That said, we leave helium carrier gas on for the unit that has a polar capillary, and cool that to 30C when not in use. The other units get the zones cooled down and the carrier gas turned off. The GCMS units get oven cooled to 40 - 70C but their carrier gas stays on.

[larkl]

I wouldn't turn it off and have never seen anyone do it. You're risking condensation in the FID and other problems already noted. If you have EPC, you can set up a shutdown method with minimal column flow. Not sure if I'd try reducing the fuel/air for the FID, maybe it'd work?

[Ron]

I keep the injector and detector hot, drop over temperature to around 50C, lower column flow to about half the flow rate I use for the analysis, run a low split ratio, maybe 5:1, and turn off the hydrogen and air. This keeps the whole system clean, and after running a blank the system should be ready to go.

[Russ]

We regularly shut down the FID gas flows after a sample run, though we use He as the carrier, and have not had any condensation issues. We also turn off the injector and detector temperature and the oven after allowing it to cool to room temp, but leave a low flow of He through the column. If you opt to shut down the carrier flow, I would download a method to allow the oven to cool to around room temp before you shut the flow off. As others have mentioned, if you leave the carrier on you can set it to a low flow.

[aldehyde]

I keep the injector and detector hot, drop over temperature to around 50C, lower column flow to about half the flow rate I use for the analysis, run a low split ratio, maybe 5:1, and turn off the hydrogen and air. This keeps the whole system clean, and after running a blank the system should be ready to go.

Do this.

As others have said if you are frequently cooling your detector to below 100 C you are risking condensation on the body and collector of the FID. I would not shut off column flow.